Process for producing porous object

ABSTRACT

The present invention provides a process for producing porous structure having similar properties to that of the porous structure produced with conventional urethane resin solution in organic solvent and suitable for artificial leather, wherein the environmental pollution in the production process with a urethane resin solution in organic solvent and adverse effect on human health caused from remained organic solvent are solved and the problems caused from nonuniform pores produced with urethane resin emulsion are solved. 
     The present invention also provides a production process for porous structure wherein an aqueous urethane resin emulsion to which a highly crystalline substance comprising of a diisocyanate and low-molecular-weight diol is added, or an aqueous emulsion of urethane resin containing the said highly crystalline substance in its polymer chain is heated and gelled with steam with the presence of a pore-forming agent for stabilizing the gel of the said aqueous urethane resin emulsion in the heating and gelling process, and then the gelled aqueous urethane resin emulsion is heated and dried for forming the space of the water into porous structure. In addition, the present invention also provides a process for producing porous structure wherein an aqueous urethane resin emulsion is heated and gelled with steam with the presence of at least one of those selected from the group comprising silica, colloidal silica, silicic acid and silicate for stabilizing the gel of the said aqueous urethane resin emulsion in heating and gelling, and is heated and dried for forming the space of the water into porous structure.

FIELD OF INVENTION

This invention relates to a process for producing porous structuresuitable for artificial leather wherein no organic solvents areemployed.

TECHNICAL BACKGROUND

In the conventional technology, artificial leather has been produced ina wet process wherein a textile product is impregnated and coated with apolyurethane resin solution in an organic solvent such asdimethylformamide (DMF) containing various additives including pigments,and then the organic solvent is extracted with water to form porousstructure; or in a dry process wherein porous structure is formed byutilizing the volatility of an organic solvent.

In those production processes, a lot of organic solvents used in theprocesses have been causing problems in work place and of environmentalpollution. In addition, those organic solvents must have been removedcompletely from resultant artificial leather. Incomplete elimination oforganic solvents gives adverse effects on workers in productionprocesses and users or wearers of products. And a lot of energy, laborand expenses have been required for preventing water and air pollutionand adverse effects on workers and wearers.

On the contrary, the solvent-free process with urethane resin emulsionrequire no recovering of organic solvents and improves workingenvironment causing no water and air pollution. And the adverse effectson workers, users and wearers due to remained organic solvents inproducts can be remarkably minimized.

The conventional processes with urethane resin emulsion, in which poresare formed with foaming, can only produce porous structure consisting ofseparated air bubbles.

Such porous structure is not suitable for artificial leather. The porousstructure that can only be produced with foaming has limited the end useand application field of the artificial leather produced with urethaneresin emulsion.

A production process for fiber sheet containing uniform microporousstructure of urethane resin and having soft handle, in which an aqueousresin composition consisting of urethane resin having carboxyl groups inits molecule, an inorganic salt, and a nonionic surfactant having aclouding point is employed for attaining the structure and handle, hasbeen disclosed in Japanese Patent Laid Open Hei 11-335975. In theprocess, the microporous structure is produced through producingcrystalline structure with water-insoluble nuclei formed withcross-linking a proper quantity of the said carboxyl groups contained inthe urethane resin molecules and the polyvalent metal ions in the saidinorganic salt, such as aluminum chloride or calcium chloride. And thequantity of the carboxyl groups contained the urethane resin molecules,in other words, the acid value of the solid portion of the urethaneresin, influences on the microporous structure and the stability of theaqueous resin composition. A sufficient quantity of carboxyl groups inthe urethane resin molecules for producing satisfactory microporousstructure deteriorates the stability of the aqueous resin composition.Thus urethane resins containing limited quantity of carboxyl groups mustbe applied for the process.

The present invention provides a process for producing porous structure,consisting of continuous pores and suitable for artificial leather, witha specific aqueous emulsion of urethane resin for the purpose ofeliminating the above-mentioned environmental pollution in theproduction process with a urethane resin solution in organic solvent andadverse effect on human health caused from remained organic solvent. Inaddition, the present invention provides porous structure that solvesthe problems caused from nonuniform pores produced with conventionalaqueous urethane resin emulsion and has a property similar to the porousstructure produced with conventional urethane resin solution in organicsolvent.

DISCLOSURE OF INVENTION

The inventors of the present invention have concentrated on the studyaiming to produce porous structure containing continuous pores withurethane resin emulsion, and finally found the procedure for attainingthe object as mentioned below with which the present invention has beencompleted. The object can be attained with an aqueous urethane resinemulsion prepared by adding highly crystalline substance consisting of adiisocyanate such as diphenylmethane diisocyanate, dicyclohexylmethanediisocyanate, or isophorone diisocyanate and a low-molecular-weight diolsuch as ethylene glycol or tetramethylene glycol to an aqueous urethaneresin emulsion, or with an aqueous urethane resin emulsion prepared byemulsifying a urethane resin produced through condensationpolymerization of urethane resin utilizing the above-mentioned highlycrystalline substance as nuclei. The said aqueous urethane resinemulsion is heated and gelled with steam in subsequent process to beformed into crystalline structure in which the said highly crystallinesubstance functions as the nuclei of the structure. Fine particles ofsilica, colloidal silica, silicic acid or silicate, especially thoseimparted with hydrophobic property, function effectively as apore-forming agent to stabilize the gel of the said aqueous urethaneresin emulsion through heating and gelling with steam. The gel is thenheated and dried to remove water for forming the space of water dropletsinto continuous pores of porous structure suitable for artificialleather.

The present invention provides a production process for porous structuresuitable for artificial leather through impregnating and coatingnonwoven fabric, woven fabric or film with an aqueous urethane resinemulsion, then heating and gelling the impregnated fabric with steam,and finally heating to remove water from the fabric. In the process, anaqueous urethane resin emulsion to which the above-mentioned highlycrystalline substance is added, or an aqueous emulsion of urethane resincontaining the said highly crystalline substance in its polymer chain isblended with the above-mentioned pore-forming agent, heated and gelledwith steam, and then heated to be dried in subsequent process. Andthrough those processing steps, the urethane resin emulsion is gelledwith the highly crystalline substance functioning as nuclei, in otherwords, converted from water soluble sol to water-insoluble gel, theurethane resin is then separated from water, and the space of theseparated water is finally formed into continuous pores in heating anddrying process to produce porous structure suitable for artificialleather.

The inventors of the present invention have completed the presentinvention also with the finding that an aqueous urethane resin emulsion,to which at least one of those selected from the group comprisingsilica, colloidal silica, silicic acid and silicate, especially thoseimparted with hydrophobic property, is added, can be formed into stablegel in which water and urethane resin are separated in steam-heating andgelling operation and then formed into porous structure suitable forartificial leather in the subsequent heating and drying wherein water isremoved to leave its space as continuous pores.

The present invention provides a production process for porous structuresuitable for artificial leather through impregnating and coatingnonwoven fabric, woven fabric or film with aqueous urethane resinemulsion, heating to gel the emulsion with steam, and finally heating todry the gel. In the process, at least one of those selected among thegroup comprising silica, colloidal silica, silicic acid and silicate,especially those imparted with hydrophobic property, is added to thesaid aqueous urethane resin emulsion, and the emulsion is heated to begelled with steam and then heated to separate the resin and water and toremove the water to form the space of the water into continuous poresafter the heating.

Further the present invention provides a process for producing porousstructure suitable for artificial leather wherein polyalkylene glycolshaving affinity to water is added to the aqueous urethane resin emulsionas a stabilizer in addition to the said preferable pore-forming agent,such as silica, colloidal silica, silicic acid and/or silicate, morepreferably silicic acid and/or silicate imparted with hydrophobicproperty, for the purpose of inhibiting water evaporation from the saidaqueous urethane resin emulsion until the gel of the urethane resinemulsion is formed in the heating and gelling with steam and theurethane portion is completed in the heating and drying process so as toform the space of water into continuous pores certainly after theheating and drying process.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the electron photomicrograph of porous structure in Example3.

FIG. 2 shows the electron photomicrograph of porous structure inComparative Example 1.

FIG. 3 shows the electron photomicrograph of porous structure in Example6.

FIG. 4 shows the electron photomicrograph of porous structure in Example11.

FIG. 5 shows the electron photomicrograph of porous structure inComparative Example 2.

FIG. 6 shows the electron photomicrograph of porous structure in Example14.

BEST MODE OF EMBODIMENT

The best mode of the present invention is exemplified in the followingdescription though the present invention is not restricted within thescope of the embodiment.

For attaining the above-mentioned object, the present invention providesa production process for porous structure wherein an aqueous urethaneresin emulsion to which a highly crystalline substance comprising of adiisocyanate and low-molecular-weight diol is added, or an aqueousemulsion of urethane resin containing the said highly crystallinesubstance in its polymer chain is heated and gelled with steam beingblended with a pore-forming agent that stabilizes the gel of the saidaqueous urethane resin emulsion in the heating and gelling process andthen the gelled aqueous urethane resin emulsion is heated and dried forleaving the space of the water into porous structure (First invention).

Further for attaining the said object, the present invention provides aprocess for producing porous structure wherein an aqueous urethane resinemulsion is heated and gelled with steam being blended with at least oneof those selected from the group comprising silica, colloidal silica,silicic acid and silicate for stabilizing the gel and is heated anddried for forming the space of the water into porous structure (Secondinvention).

[First Invention]

At first, the aqueous urethane resin emulsion used for First inventionis described.

In the production process of porous structure for artificial leatherwith an aqueous urethane resin emulsion, an aqueous urethane resinemulsion to which a highly crystalline substance comprising ofdiisocyanate, such as diphenylmethane diisocyanate (MDI),dicyclohexylmethane diisocyanate, or isophorone diisocyanate (IPDI), andof low-molecular-weight diol, such as ethylene glycol or tetramethyleneglycol, preferably having superior compatibility to urethane resin, isadded by 5 to 55 weight percent of the urethane resin, or an aqueousemulsion of urethane resin containing the said highly crystallinesubstance in its polymer chain by 5 to 55 weight percent is used. Thepreferable ratio of the urethane resin in the aqueous urethane resinemulsion is 10 to 35 weight percent.

In this specification, “a highly crystalline substance comprising ofdiisocyanate and low-molecular-weight diol” denotes a highly crystallinesubstance produced by reacting a highly crystalline diisocyanate andlow-molecular-weight diol. And “an aqueous emulsion of urethane resincontaining highly crystalline substance in its polymer chain” denotes anaqueous emulsion of urethane resin of which polymer chain (urethaneresin chain) partially consists of the said highly crystallinesubstance.

The preferable diisocyanate is highly crystalline diphenylmethanediisocyanate (MDI), dicyclohexylmethane diisocyanate or isophoronediisocyanate (IPDI) and the preferable low-molecular-weight diol isethylene glycol that is compatible to the said emulsion. The preferablemolecular weight of the low-molecular-weight diol ranges from 62 to 200.Less than 5 weight percent of the highly crystalline substance to aurethane resin cannot attain the aimed effect while more than 55 weightpercent of the said substance to a urethane resin is apt to deterioratethe property of the urethane resin due to the influence by the propertyof the said highly crystalline substance. Less than 5 weight percent ofthe highly crystalline substance in the polymer chain of a urethaneresin cannot attain the aimed effect while more than 50 weight percentof the said substance is apt to deteriorate the property of a urethaneresin due to the influence by the property of the said highlycrystalline substance.

Preferable pore-forming agent added to the aqueous urethane resinemulsion of First invention is silica, colloidal silica, silicic acid orsilicate, and the preferable ratio of the agent is 1 to 20 weightpercent of a urethane resin. The preferable silicate is an alkalinemetal salt.

Specifically preferable agent is a silicone compound that has superiorperformance for forming porous structure having continuous pores, suchas silica, colloidal silica, silicic acid or silicate of which surfaceis imparted with hydrophobic property.

Such hydrophobic property imparted to silica, colloidal silica, silicicacid or silicate is attained with chemical reaction with an organicsilicon compound, from which resultant compound is called as “reactedtype”. The organic silicon compound to be reacted with the saidsubstances is substituted silanes, such as trimethylchlorosilane,dimethylchlorosilane or monomethylchlorosilane. Dimethylchlorosilane ismost frequently used for economical reason.

In addition, hydrophobic property can also be imparted to, for example,silica by blending a suspension of silica and an organic siliconcompound, adding organic solvent to the blend and separating the silicafrom the liquid phase, from which resultant substance is called as“absorbed type”.

A pore-forming agent reacted with an organic silicon compound is morepreferable than an “absorbed type” agent because the reacted type agenthas superior pore-forming performance and the resultant pores haveuniform size.

The hydrophobic property of those agents is determined by the minimumvolume percent of methanol in an aqueous solution of methanol that canwet those agents (hereinafter referred to as M value). Preferable Mvalue for sufficient pore-forming performance is 20 volume percent ormore and the agents having M value of 45 volume percent or more areespecially preferable.

Less than 1 weight percent of a pore-forming agent to urethane resincannot attain the aimed effect while more than 20 weight percent of theagent deteriorates the property of urethane resin because the agent,silicic acid or silicate, is apt to crystallize in urethane resin.

[Second Invention]

The second invention of the present invention provides a productionprocess of porous structure wherein an aqueous urethane resin emulsionis heated and gelled with steam with the presence of at least one ofthose selected from the group comprising silica, colloidal silica,silicic acid and silicate, which stabilizes the gel of the urethaneresin emulsion in the heating and gelling step, as mentioned above, andthen dried with heating to form the space of the water into pores.

In the above process, the preferable silica, colloidal silica, silicicacid and silicate are those imparted with hydrophobic property,especially those imparted with hydrophobic property through reactionwith an organic silicon compound, because they have superior performancefor forming porous structure having continuous pores. The examples ofsuch silica, colloidal silica, silicic acid and silicate are the same asthose exemplified in the above-mentioned [First invention].

The ratio of the urethane resin contained in the aqueous urethane resinemulsion employed in the second invention of the present inventionpreferably ranges from 10 to 35 weight percent.

The ratio of at least one of those selected from the group comprisingsilica, colloidal silica, silicic acid and silicate to urethane resinpreferably ranges from 1 to 20 weight percent.

[Materials Common to First and Second Inventions]

The aqueous urethane resin emulsion employed both in the first andsecond inventions contains a stabilizer such as polyalkylene glycolhaving high affinity to water by 0.1 to 10 weight percent of urethaneresin in the emulsion. The stabilizer functions together with silica,colloidal silica, silicic acid or silicate to control rapid waterevaporation in heating and drying process to form more constantcontinuous pores.

Preferable stabilizer is a polyoxyethylene-polyoxypropylene blockcopolymer having a cloud point of 55° C. or higher in 1 weight percentaqueous solution, which does not lower its affinity to water duringheating and drying process of which temperature range includes the cloudpoint of the stabilizer. Less than 0.1 weight percent of the stabilizerto urethane resin cannot attain the aimed effect and more than 10 weightpercent results in poor quality of formed porous structure havingcontinuous pores by imparting hydrophilic property to the surface of theporous structure.

Either anionic or nonionic urethane resins can be employed for preparingthe aqueous urethane resin emulsion of the present invention accordingto the property of aimed artificial leather. And those anionic ornonionic urethane resins can also be employed for preparing the aqueousemulsion of a urethane resin containing a highly crystalline substancein its polymer chain.

[Process for Producing Porous Structure]

In the production process of the porous structure of the presentinvention, nonwoven fabrics, woven fabrics and knit fabrics employed inconventional processes can be employed as the base fabric for artificialleather. The impregnation and coating of an aqueous urethane resinemulsion can be practiced with similar machines used in conventionalproduction facilities.

In First invention, the aqueous urethane resin emulsion blended with ahighly crystalline substance can be prepared by adding a highlycrystalline substance comprising of a diisocyanate andlow-molecular-weight diol, then adding a pore-forming agent such assilicic acid imparted with hydrophobic property, preferably adding, forexample, a polyoxyethylene-polyoxypropylene block copolymer, andhomogenizing with a proper mixer.

The aqueous emulsion of a urethane resin containing a highly crystallinesubstance in its polymer chain can be prepared through the processwherein a highly crystalline substance is at first produced bycondense-polymerizing the aforementioned diisocyanate such asdiphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate orisophorone diisocyanate (IPDI), and low-molecular-weight diol, such asethylene glycol or tetramethylene glycol, in an organic solventcompatible to polyurethane, such as dimethylformamide (DMF), ethyleneglycol diethyl ether or ethylene glycol monoethyl ether acetate; thenthe produced highly crystalline substance is condense-polymerized with apolyol, such as polyoxyethylene-polyoxypropylene random copolymer,polyalkylene glycol (polytetraethylene glycols, etc.) or polyoxyethyleneglycol copolymer, and with a diisocyanate other than the diisocyanateemployed for producing the highly crystalline substance, with thepresence of, if necessary, dipolyalkylene glycol ester of a dibasic acidto be formed into a urethane resin; water is added to the resultanturethane resin; and the organic solvent is removed with distillation tomake up an emulsion. An aqueous emulsion of the urethane resincontaining the highly crystalline substance in its polymer chain canpreferably be made by adding a pore-forming agent, such as silica,colloidal silica, silicic acid or silicate imparted with hydrophobicproperty, and preferably polyoxyethylene-polyoxypropylene blockcopolymer to the above-mentioned aqueous emulsion of the said urethaneresin containing the said highly crystalline substance in its polymerchain, and by homogenizing the mixture with a mixer. In addition, aproper surfactant can also be added to the aqueous emulsion of theurethane resin containing the highly crystalline substance in itspolymer chain in the process of preparing the emulsion.

In Second invention, the aqueous urethane resin emulsion can be preparedby adding silica, colloidal silica, silicic acid or silicate beingimparted with hydrophobic property, and preferablypolyoxyethylene-polyoxypropylene block copolymer to an aqueous urethaneresin emulsion, and by homogenizing with a mixer.

A proper quantity of a viscosity improver consisting of acrylic acids orsurfactants can be added to the aqueous urethane resin emulsion of thefirst or second invention for the purpose of controlling emulsionviscosity suitable for impregnation and coating.

Heating and gelling with steam can be practiced with the parameters of anormal-pressure steamer, such as saturated steam at 60 to 100° C., andsubsequent heating and drying operation can be practiced throughdry-heating with a common tenter frame or drying with far-infraredradiation preferably at 70 to 120° C.

EXAMPLES

The present invention is further described with the following examplesthough the present invention is not restricted within the scope of thoseexamples. The “part or parts” mentioned in the following examples arepart or parts by weight unless otherwise specified.

The polyester nonwoven fabric used in the evaluation had a thickness of1.3 mm and a density of 0.27 g/cm². The properties provided by thepresent invention were evaluated in the following procedure.

Electron photomicrograph: The porous structure at the surface of theartificial leathers produced in Examples and Comparative Examples wastaken in scanning electron photomicrographs (SEM) and evaluated. TheSEMs in FIGS. 1 to 6 show the surface of artificial leather magnified150 times.

Visual inspection of porous structure: The porous structure admitted tobe the most preferable for artificial leather was marked with “⊚”,preferable with “◯”, least acceptable with “Δ”, and not applicable with“X”.

Thickness: measured with a PEACOCK Thickness Meter, Type H, produced byOzaki Seisakusho Co., Ltd., with minimum graduation of 0.01 mm

Density: evaluated in the procedure defined in JIS-K-6505

Hardness and softness: evaluated in the procedure defined in JIS-L-1079(Smaller figure indicates softer handle.)

Example 1

Five hundred milliliter of dimethylformamide (DMF) and 300 ml ofethylene glycol diethyl ether were placed in a reactor equipped with areflux condenser, an agitator, a thermometer and dropping devices, anddiphenylmethane diisocyanate (375 g or 1.5 mol) was added under nitrogengas flow. The mixture was homogenized with agitation at 40° C. or lowerand dissolved in an organic solvent. Then ethylene glycol (62 g or 1.0mol) was dropped from a dropping device into the mixture at 80° C. orlower to react with the diphenylmethane diisocyanate.

After the exothermal reaction was completed, the mixture was cooled downto 40° C. or lower and 200 ml of aqueous solution containing sodiumbisulfite (83 g or 0.52 mol) and a surfactant of POE alkyl ether havinga HLB of 12 or higher and proper emulsifying performance (10.4 g or 2weight percent of resin) was dropped from a dropping device to capnon-reacted isocyanate groups. Then 800 ml of deionized water beingconditioned at 50° C. or less was dropped in the mixture from a droppingdevice.

After the dropping, the mixture was homogenized with agitation and theorganic solvent used was removed with reduced pressure distillation fromthe reacted product. Then the water evaporated in azeotrope during thereduced pressure distillation was compensated to make up the aqueousdispersion of the highly crystalline substance to be employed in thefirst invention of the present invention.

Example 2

Five hundred milliliter of dimethylformamide (DMF) and 300 ml ofethylene glycol diethyl ether were placed in a reactor having the sameequipment as in Example 1, and diphenylmethane diisocyanate (276 g or1.1 mol) was added under nitrogen gas flow. The mixture was homogenizedwith agitation at 40° C. or lower and dissolved in an organic solvent.Then ethylene glycol (62 g or 1.0 mol) was dropped from a droppingdevice into the mixture at 80° C. or lower to react with thediphenylmethane diisocyanate.

After the exothermal reaction was completed, the mixture was cooled downto 40° C. or lower and isophorone diisocyanate (244.5 g or 1.1 mol) as adiisocyanate compound other than diphenylmethane diisocyanate,polytetramethylene glycol having a molecular weight of 1000 (500 g or0.5 mol), polyethylene glycol having a molecular weight of 600 (54 g or0.09 mol), trimethylol propane (8 g or 0.06 mol) and tetramethyleneglycol (11.8 g or 0.13 mol) were added. They were reacted with themixture at 70 to 90° C. with 0.3 g of tin octylate as a catalyst toproduce urethane prepolymer containing a highly crystalline substancethat had isocyanate groups on its molecular chain terminal.

Then 1885 g of an aqueous solution containing diethylene glycol (10 g)and piperazine (10 g) as polymer-chain extenders and POE (18) styrenatedphenol ether (40.2 g or 5 weight percent of resin) as an emulsifier wasadded to the prepolymer at 60° C. or lower for extending polymer chainand the mixture was preliminarily emulsified to make up a mixture ofurethane resin, water and organic solvent. The mixture was furtheragitated with a homogenizer to be emulsified mechanically and forcedlyand made into homogeneous emulsion.

Then the organic solvent in the above emulsion was removed with reducedpressure distillation and the water evaporated in azeotrope during thereduced pressure distillation was compensated to make up the aqueousemulsion of urethane resin containing highly crystalline substance inits polymer chain of the present invention.

Examples 3 to 10 and Comparative Example 1

For checking continuous pore structure formed in film, each of thecompositions listed in Table 1 was coated on polyester film of100-micrometer thickness with 1.0-mm clearance, heated and gelled withsaturated steam at 90° C. for 30 minutes, and heated and dried with dryair at 95° C. for 60 minutes to be processed into film on which porousstructure was layered.

TABLE 1 Tests on Film Components (parts by weight) and evaluation ofporous Comparative Example Example Example Example Example ExampleExample Example structure Example 1 3 4 5 6 7 8 9 10 SUPERFLEX E-2000 8080 56 80 56 80 80 Dispersion of highly crystalline 30 30 substance with40-% concentration in Example 1 Urethane resin emulsion having 100 100highly crystalline substance in polymer chain with 40-% concentration inExample 2 Colloidal silica 10 10 10 Hydrophobic silicic acid 2 2 2(reacted type) Hydrophobic silica 2 (reacted type) Hydrophobic silica 2(absorbed type) Polyalkylene glycols 5 5 5 5 5 5 5 5 SDK 5 5 5 5 5 5 5 55 Water 120 120 114 100 120 114 100 100 100 Porous state Non-porousPorous Porous Porous Porous Porous Porous Porous Porous (Words in theparentheses X (FIG. 2) Δ (FIG. 1) ◯ ◯ ⊚ (FIG. 3) ⊚ ⊚ ⊚ ◯ indicate thenumber of figures showing SEM.) Thickness (mm) 0.28 0.52 0.75 0.77 0.680.77 0.78 0.80 0.64 Density (g/cm³) 0.779 0.659 0.472 0.472 0.474 0.4680.462 0.465 0.470 Hardness and softness (mg) 77 56 59 54 63 52 53 52 53The components in Table 1 and in Tables 2 to 4 described below are asfollows.

SUPERFLEX E-2000: forcibly emulsified nonionic urethane resin emulsionproduced by Dai-Ichi Kogkyo Seiyaku Co., Ltd., with 50-% concentrationand a pH of 6 to 8, producing dried film of which 100-% modulus is 7 MPa

Highly crystalline substance described in Example 1 of the presentinvention, containing 40% of highly crystalline substance

Emulsion of urethane resin containing highly crystalline substance inits polymer chain described in Example 2 of the present invention,containing 40% of urethane resin

Colloidal silica: produced by Nissan Kagaku Kogyo Co., Ltd., with thetrade name of SNOWTEX with an M value of 0%

Hydrophobic silicic acid: produced by Matsumoto Yushi-Seiyaku Co., Ltd.,with the trade name of Silicic Acid H with an M value of 45%

Hydrophobic silica (reacted): produced by Nippon Silica Kogyou Co.,Ltd., with the trade name of Nipsil SS-178B, with an M value of 60%

Hydrophobic silica (absorbed): produced by Matsumoto Yushi-Seiyaku Co.,Ltd., with the trade name of Silica SS with an M value of 40%

Polyalkylene glycols: nonionic polyalkylene glycol block copolymerproduced by adding ethylene oxide to polypropylene glycol (2000molecular weight) to a ratio with which ethylene oxide is contained 80weight percent of the resultant glycol, of which 1-% solution has acloud point of 100° C. or higher, with 100% concentration

SDK: a nonionic viscosity improver produced by Matsumoto Yushi-SeiyakuCo., Ltd., with 100% concentration

Examples 11 to 17 and Comparative Example 2

Polyester nonwoven fabric having a thickness of 1.3 mm and a density of0.27 g/cm² was immersed in a solution prepared by adding 3 weightpercent of methylhydrogen polysiloxane emulsion (produced by MatsumotoYushi-Seiyaku Co., Ltd. with the trade name of GERANEX S-3) and 1 weightpercent of a zinc compound emulsion, which was the catalyst of the saidpolysiloxane, (produced by Matsumoto Yushi-Seiyaku Co., Ltd. with thetrade name of Catalyst TSC-450), squeezed with a mangle to removeexcessive solution and dried at 120° C. to be made into pre-treatednonwoven fabric (silicone-treated nonwoven fabric).

After squeezing with a mangle, the quantity of the solution remained inthe nonwoven fabric was 130 weight percent of the fabric, in otherwords, 130 g of the solution remained in 100 g of the nonwoven fabric.

Then the pre-treated nonwoven sample was coated with each of thecompositions in Table 2 with 1.0-mm clearance, treated in heating andgelling with saturated steam at 90° C. for 30 minutes, and dried withdry heating at 95° C. for 120 minutes to be formed into a fabric likeartificial leather.

TABLE 2 Tests on Silicone-Treated Nonwoven Fabric Components (parts byweight) and Comparative Example Example Example Example Example ExampleExample evaluation of porous structure Example 2 11 12 13 14 15 16 17SUPERFLEX E-2000 80 80 56 80 56 80 Dispersion of highly crystalline 3030 substance with 40-% concentration in Example 1 Urethane resinemulsion having highly 100 100 crystalline substance in polymer chainwith 40-% concentration in Example 2 Colloidal silica 10 10 10Hydrophobic silicic acid (reacted type) 2 2 2 Hydrophobic silica(reacted type) 2 Polyalkylene glycols 5 5 5 5 5 5 5 SDK 5 5 5 5 5 5 5 5Water 120 120 114 100 120 114 100 100 Porous state Non-porous PorousPorous Porous Porous Porous Porous Porous (Words in the parenthesesindicate the X (FIG. 5) Δ (FIG. 4) ◯ ◯ ⊚ (FIG. 6) ⊚ ⊚ ⊚ number offigures showing SEM.) Thickness (mm) 1.37 1.83 2.08 2.01 2.11 2.23 2.272.25 Density (g/cm²) 0.435 0.396 0.388 0.379 0.378 0.376 0.376 0.374Hardness and softness (mg) 490 510 520 510 510 510 520 510

Examples 18 to 20 and Comparative Example 3

Polyester nonwoven fabric having a thickness of 1.3 mm and a density of0.27 g/cm² was immersed in a solution prepared by adding 3 weightpercent of methylhydrogen polysiloxane emulsion (produced by MatsumotoYushi-Seiyaku Co., Ltd. with the trade name of GERANEX S-3) and 1 weightpercent of a zinc compound dispersion, which was the catalyst of thesaid polysiloxane, (produced by Matsumoto Yushi-Seiyaku Co., Ltd. withthe trade name of Catalyst TSC-450), squeezed with a mangle to removeexcessive solution and dried at 120° C. to be made into pre-treatednonwoven fabric.

After squeezing with a mangle, the quantity of the solution remained inthe nonwoven fabric was 130 weight percent of the fabric weight, inother words, 130 g of the solution remained in 100 g of the nonwovenfabric.

Then the pre-treated nonwoven sample was impregnated with each of thecompositions in Table 3, treated in heating and gelling with saturatedsteam at 90° C. for 30 minutes, and dried with dry heating at 95° C. for120 minutes to be made into a test fabric containing urethane resin.

TABLE 3 Urethane Resin Impregnation in Nonwoven Fabric Components (partsComparative Example Example Example by weight) Example 3 18 19 20SUPERFLEX E-2000 80 80 56 Dispersion of highly 30 crystalline substancewith 40-% concen- tration in Example 1 Urethane resin emul- 100 sionhaving highly crystalline substance in polymer chain with 40-%concentration in Example 2 Colloidal silica 10 10 10 Polyalkyleneglycols 5 5 5 SDK 5 5 5 5 Water 170 170 164 150

Examples 21 to 27 and Comparative Example 4

The nonwoven fabric containing urethane resin described in the aboveComparative Example 3 was coated with each of the compositions in Table4 with 1.0-mm clearance, treated in heating and gelling with saturatedsteam at 90° C. for 30 minutes, and dried with dry heating at 95° C. for120 minutes to be formed into a fabric like artificial leather.

TABLE 4 Tests on Urethane-Resin-Impregnated Nonwoven Fabric Components(parts by weight) Comparative Example Example Example Example ExampleExample Example and evaluation of porous Example 4 21 22 23 24 25 26 27structure Comparative Example Example Example Example Example ExampleExample Impregnate fabric tested Example 3 18 19 20 18 19 20 18SUPERFLEX E-2000 80 80 56 80 56 80 Dispersion of highly crystalline 3030 substance with 40-% concentration in Example 1 Urethane resinemulsion having 100 100 highly crystalline substance in polymer chainwith 40-% concentration in Example 2 Colloidal silica 10 10 10Hydrophobic silicic acid 2 2 2 (reacted type) Hydrophobic silica 2(reacted type) Polyalkylene glycols 5 5 5 5 5 5 5 SDK 5 5 5 5 5 5 5 5Water 120 120 114 100 120 114 100 100 Porous state Non-porous PorousPorous Porous Porous Porous Porous Porous X Δ ◯ ◯ ⊚ ⊚ ⊚ ⊚ Thickness (mm)1.49 1.97 2.16 2.11 2.19 2.22 2.21 2.20 Density (g/cm³) 0.491 0.4690.428 0.446 0.435 0.428 0.430 0.431 Hardness and softness (mg) 760 730740 740 740 740 750 740

FIELD OF APPLICATION

The process of the present invention can solve the troubles found in theprocesses with urethane resin solution in organic solvent owing to theabove-mentioned aqueous urethane resin emulsion employed in the saidprocess. In addition, the process of the present invention can provideideal porous structure for producing low-density bulky porous structurecontaining continuous foamy pores and suitable for artificial leather,which is lighter and softer than the porous structure produced inprocesses other than the present invention.

1. A process for producing a porous structure, wherein an aqueousurethane resin emulsion, to which a highly crystalline substancecomprising a diisocyanate and low-molecular-weight diol is added, or anaqueous emulsion of urethane resin containing the highly crystallinesubstance in its polymer chain is heated and gelled with steam with thepresence of a pore-forming agent for stabilizing the gel of the saidaqueous urethane resin emulsion in the heating and gelling, and heatedand dried for forming the space of water into pores, wherein the aqueousurethane resin emulsion contains 61.5% to 89.99% by weight of water. 2.The process in claim 1 wherein the said pore-forming agent is at leastone of silica, colloidal silica, silicic acid and silicate.
 3. Theprocess in claim 2 wherein the said silica, colloidal silica, silicicacid and silicate are hydrophobic.
 4. A process for producing a porousmaterial wherein an aqueous urethane resin emulsion containing 61.5% to89.99% by weight of water is heated and gelled with steam with thepresence of at least one of those selected from the group comprisingsilica, colloidal silica, silicic acid and silicate for stabilizing thegel of the said aqueous urethane resin emulsion in the heating andgelling with steam, and heated and dried for forming the space of waterinto pores.
 5. The process in claim 4 wherein the said silica, colloidalsilica, silicic acid and silicate are hydrophobic.
 6. The process inclaim 1, wherein a density of the porous structure is from 0.35 to 0.50g/cm³.
 7. The process in claim 4, wherein a density of the porousmaterial is from 0.35 to 0.50 g/cm³.
 8. The process in claim 1, whereina pore-forming agent and a stabilizer are contained in the aqueousurethane resin emulsion.
 9. The process in claim 8, wherein thestabilizer is a polyalkylene glycol having a cloud point of 55° C. orhigher as an aqueous 1 wt. % solution thereof.
 10. The process in claim4, wherein a pore-forming agent and a stabilizer are contained in theaqueous urethane resin emulsion.
 11. The process in claim 10, whereinthe stabilizer is a polyalkylene glycol having a cloud point of 55° C.or higher as an aqueous 1 wt. % solution thereof.
 12. The process inclaim 1, wherein the water content is 74 to 82% by weight.
 13. Theprocess in claim 4, wherein the water content is 74 to 82% by weight.